Changes in gene expression associated with the differentiation of murine embryonal carcinoma cells to extraembryonic endoderm will be investigated by direct electrophoretic analysis of the H1 histones and nonhistone, nuclear-associated proteins, cellular hybridization experiments and the development of a microinjection assay for activities suggested to be in endodermal cells capable of causing embyronal carcinoma to differentiate. The extinction of one of five subtypes of the H1 histones may be correlated with the differentiation of embryonal carcinoma cells to parietal endoderm. The distribution of H1 subtypes in the chromatin of embryonal carcinoma cells and endodermal cells will be investigated by the isolation of monoclonal antibodies specific for each H1 subtype. The antibodies will be used to fractionate chromatin by affinity chromatography and the resulting DNA fractions will be analyzed by DNA-DNA hybridization. An endodermal, nuclear-\ associated, basic, 50,000 M.W. protein will be purified for use as an antigen. Specific antisera will be used to confirm the cellular location of the antigen, its distribution among different differentiated cell types, and the kinetics of its induction after embryonal carcinoma cells are induced to differentiate. Activities responsible for the extinction of embryonal carcinoma functions and the possible activation of endodermal functions in cellular hybrids between embryonal carcinoma cells and parietal endodermal cells will be studied in hybrids between human choriocarcinoma cell lines and murine embryonal carcinoma cells. Parietal endodermal cells will be fractionated, concentrated and microinjected into embryonal carcinoma cells to determine if activities can be detected which will cause embryonal carcinoma cells to differentiate.